Gas Appliances (CO Sensors)

This page contains the work that CPSC has done with voluntary standards involving gas appliances and CO sensors.

The U.S. Consumer Product Safety Commission (CPSC) staff participates in voluntary standards activities to address carbon monoxide (CO) hazards associated with vented gas heating appliances, such as furnaces and boilers. The Canadian Standards Association (CSA) and CSA America, Inc. (operating as CSA Group) develop voluntary standards for gas appliances and gas appliance accessories sold in the U.S. and Canada. The U.S. versions of these standards are accredited by the American National Standards Institute (ANSI), while the Canadian versions are accredited by the Standards Council of Canada.

The staff has worked with the American National Standards Institute (ANSI) Z21/83 Technical Committee to develop a performance requirement that appliances shut down, or exhibit some other preemptive response, when dangerous levels of CO within the appliance are detected. The scope of this project includes vented residential gas heating appliances, such as gas furnaces, boilers, floor furnaces, and wall furnaces, that use natural gas or liquefied petroleum gas (LP-gas) for fuel. If these products are not properly installed or maintained, or if they experience component malfunction or defect, they may not burn their fuel completely, resulting in the production of dangerous levels of CO.

When CPSC staff reviews information reported during In-Depth Investigations (IDIs) involving CO exposure and vented gas appliances, the most commonly reported failure mode or condition that led or contributed to the incident was a blocked or disconnected, breached, or hole in the vent pipe, chimney, or heat exchanger. CPSC staff has made a number of proposals to the ANSI/CSA standards groups to address CO incidents caused by these conditions. In 1997, CPSC staff proposed that the ANSI Z21.47 central furnace subcommittee adapt requirements that gas furnaces:

1. Shutdown when the vent pipes became disconnected; and

2. Shutdown when the vent pipe became totally or partially blocked.

To support that proposal, CPSC staff conducted testing and analysis from 1999 to 2000, of CO emissions from gas furnaces to determine the concentrations of CO that could be generated under conditions reported in CO poisoning incidents and the associated health affects at those levels. In 2000, CPSC staff presented these test and analysis results to the ANSI Z21.47 Central Furnace Subcommittee with a proposal that the following performance requirements be added to the Z21.47 central furnace standard to require that a furnace:

1. Shutdown when the vent pipe became disconnected; and

2. Shutdown when the vent pipe became totally or partially blocked; or

3. Be equipped with a means to prevent furnace CO emissions from exceeding the standard limits once

installed in the field; or

4. Be equipped with a means to shutdown when furnace CO emissions exceeded the standard limits.

To support proposals 3) and 4), in 2000 CPSC staff began an investigation of combustion gas sensing technologies that might be used to detect CO in gas appliance flue passageways and provide a shutoff or other preemptive response to dangerous levels of CO. In 2001, staff acquired CO sensing technologies, integrated them into the vent pipe and control of a gas furnace and successfully demonstrated the concept of using the sensors to detect CO levels in excess of 400 ppm in the vent pipe and shutdown the furnace in response. In 2001, CPSC staff presented these test results to the ANSI Z21.47 central furnace subcommittee. In 2002, in response to CPSC staff’s “CO shutoff proposal”, the ANSI Z21/83 Technical Committee (the parent committee for all ANSI Z21 gas appliances and accessory standards) established the ANSI Z21/83 Ad Hoc Working Group (AHWG) for Carbon Monoxide/Combustion Sensors. The purpose of the ANWG was to develop a test criterion and work plan to evaluate the use of sensors for a wide variety of vented gas heating appliances, including gas furnace. The AHWG completed a test criterion and work plan and submitted it to the ANSI Z21/83 Technical Committee (TC) for approval. The Z21/83 TC approved the test criterion and work plan in 2004, but did not send it out for bid by prospective test laboratories until the ANSI Z21/83 Advisory Council (AC) could fund the project. In early 2005 the Z21/83 AC sought support from various industry stakeholders, including the CPSC, to fund the project. At their fall 2005 meeting, the Z21/83 TC opted not to fund the project due to concerns raised by its members that there were no sensors commercially available that:

1. Had the durability to operate within the harsh environment of a furnace flue passageway, heat exchanger,

or vent pipe; or

2. Had the adequate longevity to survive the lifetime of a gas furnace (i.e., 15 to 20 years).

In 2006, CPSC developed a test program to address the durability and longevity concerns raised by the Z21/83 TC. The test program utilized those portions of the test criterion, developed by the Z21/83 AHWG in 2004, staff felt best addressed sensor durability and longevity. This test program was conducted from 2007 through 2008 and demonstrated that commercially available sensors were:

2. Demonstrated potential of surviving in that environment for the lifespan of the appliance.

The report of staff’s findings was delayed until 2012 due to slack resources within CPSC brought on by CPSIA. CSPC staff shared the report with the Z21/83 TC, as well as the Z21.47 central furnace Technical Advisory Group (TAG, formerly known as a “subcommittee”) and the Z21.13 boiler TAG.

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